OK, I've searched on this as I'm sure it's been done before, but I couldn't find any thing. I have Windows XP in Boot Camp. I decided to try out VMWare Fusion and Parallels. Each seemed fine on its own, running off Boot Camp. Then I wondered if I could have two instances of Windows XP both running at the same time. So I fired up Fusion and Parallels at the same time, both running off Boot Camp. At first it seemed fine and I was well pleased, then within a few minutes, Windows collapsed into a shuddering twitching heap. Now neither will startup its windows virtual machine. Restarting my macbook in BootCamp gives me a startup error: "Windows could not start because the following file is missing or corrupt: <windows root>\system32\hal.dll Please re-install a copy of the above file" Is my Bootcamp utterly borked and needs to be reinstalled? Am surprised that both Parallels / Fusion are unable to detect if others programs are using Bootcamp at the same time.